The firefighters' union claims a report revealing only 47% of England's fire authorities are performing well may "unnecessarily alarm" people.
The union claims the report fails to cover responses to emergencies
The Audit Commission rated the Isle of Wight and Lincolnshire as the two worst performers. London was one of the best.
Authorities were assessed on fire prevention and budgets, and rated excellent, good, fair, poor or weak.
The Fire Brigades Union (FBU) said the report did not cover responses to emergency incidents.
The union added "nine out of 10 people trapped in fires were being brought out alive".
It added the ability of firefighters to rescue people was "directly linked to the speed of the response and the numbers of firemen and women involved".
Matt Wrack, FBU general secretary, said: "The Audit Commission has missed the real point about what the fire service is here to do and this report could cause unnecessary alarm to the public.
"Rescues are playing a key role in driving down fire deaths to a 45-year low but the Audit Commission wrongly attributes this achievement solely to community fire safety.
"The public judge us by how quickly we respond, how many rescues we carry out and how we deal with other major emergencies but this report deals with none of those crucial issues."
The commission also described the performance of fire authorities as "patchy".
Steve Bundred, chief executive of the Audit Commission, said: "Fire and rescue authorities are changing and they must increase the momentum of progress towards modernisation.
"Fire authorities can accelerate the pace of change by addressing areas such as leadership, diversity and working conditions and practices."
Changes being made to the 47 fire authorities in England are aimed at fire prevention and follow the firefighters' pay dispute.
Councillor Les Byron, chairman of the Fire Services management committee, said: "There is great progress being made but there is recognition that there is still more work that can be done to make the fire service as responsive and efficient as possible."